As is known, there are today available numerous systems for stimulation of biological tissues, such as, for example, systems for stimulation of the human body. For instance, retinal prostheses are today available, which are electronic systems having medical purposes for people suffering from problems of eyesight.
In general, a retinal prosthesis fulfills the function of making up, at least in part, for a reduced functionality of the retina caused by a pathological condition of the retina itself, such as, for example, retinitis pigmentosa.
In greater detail, retinal prostheses may be divided into retinal prostheses of an epi-retinal type and retinal prostheses of a sub-retinal type. In use, prostheses of an epi-retinal type are set, at least in part, on the surface of the retina that is exposed to light, thus on the surface of the retina facing the crystalline lens. Instead, prostheses of a sub-retinal type are set, at least in part, between the inner retina (more in particular, the layer of bipolar cells) and the so-called retinal pigment epithelium, which is the layer of pigmented cells that is located on the outside of the retina itself.
This having been said, irrespective of the type, retinal prostheses each comprise a respective internal unit and a respective external unit. In use, the external unit is set outside the eye, whereas the internal unit is set inside the eye, and in particular within the vitreous body.
By way of example, FIG. 1A shows a retinal prosthesis 1, the external and internal units of which are designated, respectively, by 2 and 4.
The external unit 2 comprises a transmitter 6 and a first antenna 8, which is electrically connected to the transmitter 6 and is formed, for example, by a coil of conductive material.
The internal unit 4 comprises a second antenna 10, which is also formed, for example, by a coil of conductive material. Furthermore, the internal unit 4 comprises an integrated electronic device 12 and an electrical connection cable 14, which connects the second antenna 10 and the integrated electronic device 12; for example, the electrical connection cable 14 may be a flexible electrical bus.
The integrated electronic device 12 functions as artificial retina and comprises a plurality of photodetectors 18 (FIG. 1B), an electronic circuitry 19 (FIG. 2), and a plurality of electrodes 20.
As illustrated in greater detail in FIG. 1B, the integrated electronic device 12 substantially has the shape of a parallelepiped and has a bottom surface 12a and a top surface 12b. The photodetectors 18 extends out onto the top surface 12b in such a way that they may be reached by the light coming from outside, whereas the electrodes 20 extend underneath the bottom surface 12a. In turn, the bottom surface 12a is constrained, for example by an appropriate adhesive layer (not illustrated), to the electrical connection cable 14, which, in practice, carries the integrated electronic device 12.
As illustrated in greater detail in FIG. 2, the electronic circuitry 19 is electrically connected to the photodetectors 18 and to the electrodes 20. In addition, the electrical connection cable 14 comprises at least one first conductive element 14a and one second conductive element 14b, and an insulating sheath 14c, which envelops the first and second conductive elements 14a, 14b. The first and second conductive elements 14a, 14b are electrically connected to the electronic circuitry 19, for example, by a first via 21a and a second via 21b. Further, the first and second conductive elements 14a, 14b are electrically connected, respectively, to a first terminal and a second terminal of the second antenna 10. In addition, the electrodes 20 traverse the electrical connection cable 14 without electrically contacting the first and second conductive elements 14a, 14b, but rather contacting just the insulating sheath 14c. Furthermore, the electrodes 20 extend through the adhesive layer arranged between the bottom surface 12a and the insulating sheath 14c, if present.
As mentioned previously and as is illustrated in FIG. 1A, in use the external unit 2 is set in the proximity of the eye, located inside which is the internal unit 4. For instance, the external unit 2 may be mounted on a pair of spectacles in such a way that the first antenna 8 is arranged within a lens of the pair of spectacles, and in particular is arranged along the rim of said lens for enabling light to penetrate into the eye. The transmitter 6 may be carried by one arm of the spectacles.
The internal unit 4 is set within the eye in such a way that the second antenna 10 is arranged in the proximity of the crystalline lens, possibly surrounding part of the lens itself.
The integrated electronic device 12 is set in the proximity of the retina of the eye, and in particular is set in such a way that the electrodes 20 contact a portion of retina traversed by the optical axis of the crystalline lens, opposite to the pupil and including the so-called macula. Finally, the electrical connection cable 14 is set for running along the inner wall of the eyeball, without crossing the optical axis of the crystalline lens.
In greater detail, the second antenna 10 is set for not obstructing the path of the light rays that traverse the crystalline lens, and thus for enabling the light that penetrates through the lens to reach the retina. Consequently, the second antenna 10 is set for surrounding the optical axis of the crystalline lens. In practice, in the case where the second antenna 10 is precisely formed by a coil of conductive material, the axis of said coil coincides, to a first approximation, with the optical axis of the crystalline lens, which, among other things, intercepts the integrated electronic device 12.
In this way, light coming from outside traverses the crystalline lens without undergoing significant alterations on account of the presence of the second antenna 10 and impinges upon the photodetectors 18, which generate corresponding electrical signals, which in turn are supplied to the electronic circuitry 19. On the basis of the electrical signals supplied by the photodetectors 18, the electronic circuitry 19 generates, on the electrodes 20, corresponding electrical stimulating signals, which stimulate electrically the portion of retina in contact with the electrodes 20. For instance, the electrodes 20 stimulate the so-called inner retina (designated by 22 in FIG. 1B), which is formed, among other things, by the ganglion cells, the axons of which form the optical nerve. In this way, the retinal prosthesis 1 makes up, at least in part, for a possible reduced functionality of the so-called photoreceptor cells (designated by 24 in FIG. 1B), which include the cones and the rods. Since the ganglion cells are located between the photoreceptor cells 24 and the electrodes 20, the electrical stimulating signals do not traverse the photoreceptor cells 24, but rather directly stimulate the optical nerve.
In order to supply the integrated electronic device 12, the transmitter 6 generates a supply signal of an electromagnetic type, which is radiated by the first antenna 8 and is received by the second antenna 10 in such a way that, after prior propagation along the electrical connection cable 14, the supply signal reaches the integrated electronic device 12, supplying thereto the power necessary for its operation.
In greater detail, according to the frequency of the supply signal and to the distance between the first and second antennas 8, 10, between the latter a coupling of a magnetic or electromagnetic type is formed in such a way that a transfer of electric power occurs from the first antenna 8 to the second antenna 10. The electric power present on the second antenna 10 is then transferred to the integrated electronic device 12. In greater detail, in the particular case of a magnetic coupling, the first and second antennas 8, 10 function as the primary winding and secondary winding of a transformer.
Retinal prostheses similar to the retinal prosthesis 1, thus of an epi-retinal type, are described in Watanabe T. et al., “Novel Retinal Prosthesis System with Three Dimensionally Stacked LSI Chip”, European Solid-State Device Research Conference, 2006 (incorporated by reference), or else in U.S. Pat. No. 6,976,998 (incorporated by reference).
Furthermore, retinal prostheses are known of the type described in United States Patent Application Publication No. 2006/0282128 (incorporated by reference), where the external unit comprises a system for acquisition and processing of images, which are transmitted to the internal unit by coupling between the first and second antennas. In this case, the integrated electronic device may not comprise any photodetector.
There are likewise known retinal prostheses, and more precisely sub-retinal prostheses, of the type described in U.S. Pat. No. 7,483,750 (incorporated by reference), where the electrodes are set between the inner retina and the outer retina.
Once again with reference to the retinal prosthesis 1, it renders possible to make up, at least in part, for a reduced functionality of the photoreceptor cells 24. However, in the case where the integrated electronic device 12 gets damaged and has to be replaced, it becomes necessary to extract from the eye the entire internal unit 4, which entails the need to carry out a very invasive intervention, which may entail damage to the eye.
There is a need to provide an implantable system that will enable the drawbacks of the known art to be overcome at least in part.